Before bleaching one’s teeth, they should have a thorough dental examination by their dentist. One would not want to place bleach over cavities. The bleaching process many times will cause the teeth to be sensitive, so placing bleach into a cavity could increase the sensitivity. Bleaching is also not recommended for children under 16 because their pulp chamber in the center of the teeth where the nerves reside are very large which could make for extremely sensitive teeth. The peroxide ion has been shown to give off oxygen free radicals which have been shown to cause tissue damage. That is something I would not want to take a chance with in a growing child. Other issues include the possibility of gum irritation. The bleaching solutions, especially at the higher concentrations, can be somewhat caustic, and can injure the gums. Most of the time, it is just a temporary reddening and discomfort. This can be reduced by cutting the bleaching time or by switching to a weaker concentration of the bleaching solution. Both sensitivity and gum irritation tend to go away when the bleaching is stopped.